1. Field of the Invention
The present invention relates to an injection quantity control system for an internal combustion engine for correcting an injector individual difference, an inter-cylinder injection quantity variation and an injector aging deterioration quantity in an injection quantity correction value for each cylinder of the engine or in an energization period correction value for an electromagnetic valve of an injector. Specifically, the present invention relates to a pilot injection quantity control system capable of performing a small quantity of pilot injection at least once before main injection by driving the electromagnetic valve of the injector by a plurality of times in compression stroke and expansion stroke of the engine.
2. Description of Related Art
Conventionally, there is a known common rail type fuel injection system for injecting high-pressure fuel, which is accumulated in a common rail, into each cylinder of a multi-cylinder diesel engine. In the common rail type fuel injection system, a small quantity of pilot injections are performed by a plurality of times before main injection, which can generate engine torque, so that combustion noise or engine vibration are reduced and exhaust gas performance is improved by performing stable combustion from the start of the main injection. The pilot injections are performed by driving the electromagnetic valve of the injector by a plurality of times in a compression stroke and an expansion stroke of the engine.
In the control of the fuel injection quantity injected into the cylinder of the engine, a command injection quantity is calculated in accordance with engine rotation speed and accelerator position. Then, an injection quantity command value is calculated in accordance with the command injection quantity and fuel injection pressure. Then, the electromagnetic valve of the injector is driven in accordance with the injection quantity command value. Variation in an actual injection quantity relative to the injection quantity command value is regulated through individual adjustment or the like of the injector of each cylinder.
However, the fuel quantity injected in the pilot injection is as very small as mainly 5 mm3/st or smaller. Therefore, there is a possibility that the pilot injection may vanish or become excessive due to an injector individual difference, variation in the actual injection quantity with respect to fuel injection command pulse period (inter-cylinder injection quantity variation), or a deterioration in performance (function) of the injector with an aging change or the like (injector aging deterioration). As a result, an effect of the pilot injection cannot be achieved sufficiently.
As a measure to the above problem, injection quantity correction is performed in rotation speed variation inter-cylinder injection quantity correction (FCCB correction) and idling rotation speed injection quantity correction (ISC correction), which are publicly known methods. The injection quantity is corrected in accordance with the injector individual difference, the inter-cylinder injection quantity variation and the injector aging deterioration quantity. In this case, a correction value is calculated by proportionally dividing a sum of an ISC correction value and an FCCB correction value for each injection per combustion of multi-injection, in accordance with a total of the pilot injection quantity and the main injection quantity.
Therefore, if an injection quantity demanded by the engine in idling operation (engine-demanded injection quantity) includes an increase due to an engine load factor, the injection quantity correction value will include the increase of the engine-demanded injection quantity due to the engine load factor other than the injector individual difference, the inter-cylinder injection quantity variation and the injector aging deterioration quantity. Thus, the injection quantity correction value for each injection per combustion in the multi-injection may be erroneously corrected (erroneously learned). Accordingly, an excessive injection quantity correction value may be calculated with respect to an inherently required learning value. As a result, the excessive correction value obtained through the erroneous learning will pose problems of deterioration in the combustion noise, engine vibration, emission or the like.
It is therefore an object of the present invention to provide an injection quantity control system for an internal combustion engine capable of discriminating an injector individual difference, an inter-cylinder injection quantity variation and an injector aging deterioration quantity from change of engine-demanded injection quantity due to an engine load factor. Thus, erroneous correction of a correction value for each injection per combustion in multi-injection can be prevented.
According to an aspect of the present invention, when a predetermined operating state or a predetermined operating condition of an engine is detected, an injection frequency per combustion in multi-injection is switched to K times and a command injection quantity is divided into K times injections for each cylinder. While performing the K times divided injections, a variation in a rotation speed of each cylinder of the engine is detected. The detected value of the rotation speed variation of each cylinder is compared with an average value of rotation speed variations of all the cylinders. An injection quantity of each injection for each cylinder is individually corrected to smooth the rotation speed variations of the respective cylinders. While performing the K times divided injections, an average engine rotation speed is detected to compare with a target rotation speed set in accordance with the operating state of the engine. The injection quantity of each injection is corrected uniformly for all the cylinders to maintain the average engine rotation speed to the target rotation speed.
When the predetermined operating state or the predetermined operating condition of the engine is detected, the injection frequency per combustion in multi-injection is switched to N times and the command injection quantity is divided into N times injections for each cylinder. While performing the N times divided injections, a variation in the rotation speed of each cylinder of the engine is detected. The detected value of the rotation speed variation of each cylinder is compared with an average value of rotation speed variations of all the cylinders. The injection quantity of each injection for each cylinder is individually corrected to smooth the rotation speed variations of the respective cylinders. While performing the N times divided injections, an average engine rotation speed is detected to compare with the target rotation speed set in accordance with the operating state of the engine. The injection quantity of each injection is corrected uniformly for all the cylinders to maintain the average engine rotation speed to the target rotation speed.
When the injection frequency per combustion in multi-injection is switched to K times, a first correction value of each cylinder corresponding to a deviation between the detected value of the rotation speed variation of each cylinder and the average value of the rotation speed variations of all the cylinders is calculated. Meanwhile, a second correction value, which is uniform for all the cylinders necessary for maintaining the average engine rotation speed to the target rotation speed, is calculated. When the injection frequency per combustion in multi-injection is switched to N times, a third correction value of each cylinder corresponding to a deviation between the detected value of the rotation speed variation of each cylinder and the average value of the rotation speed variations of all the cylinders is calculated. Meanwhile, a fourth correction value, which is uniform for all of the cylinders necessary for maintaining the average engine rotation speed to the target rotational speed, is calculated.
A first injection quantity command value is calculated by adding the first correction value of each cylinder and the second correction value uniform for all of the cylinders to an injection quantity command value. The injection quantity command value is calculated in accordance with a command injection quantity set in accordance with a predetermined operating state or a predetermined operating condition of the engine and fuel injection pressure. A second injection quantity command value is calculated by adding the third correction value of each cylinder and the fourth correction value uniform for all the cylinders to the injection quantity command value. An injector individual difference, an inter-cylinder injection quantity variation, and an injector aging deterioration quantity are discriminated from a variation in an engine-demanded injection quantity based on a difference between the first injection quantity command value and the second injection quantity command value.
Thus, excessive correction of the correction value for each injection per combustion in multi-injection due to erroneous learning and erroneous correction or excessive learning and excessive correction can be prevented. Therefore, combustion noise, engine vibration or deterioration in exhaust gas performance (exhaust emission) of the engine 1 can be prevented. Furthermore, the variation in the engine-demanded injection quantity, particularly the variation in the engine-demanded injection quantity due to the engine load factor can be discriminated from the injector individual difference, the inter-cylinder injection quantity variation and the injector aging deterioration quantity. Therefore, the state in which the engine load such as electric load is applied can be detected. As a result, the injection quantity correction value (learning value) corresponding to the injector individual difference, the inter-cylinder injection quantity variation and the injector aging deterioration quantity can be calculated, without including the variation in the engine-demanded injection quantity due to the engine load factor. Thus, aimed injection quantity or injector energization pulse period can be continuously provided until the next calculation of the learning value. As a result, the engine performance deterioration is inhibited.